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JVC HA-M750 Mod

  1. kalbee
    Alright! So I've actually done this mod a while ago... I finally got myself to take the pictures so here goes.
    Before I get started though, I am guessing there are very little of these guys left. The plastic hinges used on these headphones are rather brittle; a good number of owners might have already broken them. Mine's are on the verge of.. Either I refashion some in wood (unlikely), or try to make something out of K'nex eventually [​IMG]
    So these headphones actually sound rather pleasing. They are on the bassy side, and are really easy to drive. The problem is the bass bleeds and overall makes the sound muddy, veiled. This mod won't fix the problem completely, but I do believe they make a pretty good improvement. So for all those that already own a pair... feel free to try! It's reversible!
    For those who do not know, this is the HA-M750
    Notice that these have cables from both sides... this makes modding them so much easier! So for starters, let's remove one of the cups for workability.
    The screws are kind of hard to remove at first. The trick is to get a larger screwdriver and press against it while turning it. Pressing hard against it will be almost essential for every screw, whether fastening them on or removing them. Once the screw removed, use a thin flat head driver to wedge it out. You will only get about the same amount out as in the picture above.
    Notice the part where the stainless steel band joins the plastic? Push that part in to get the cover off. In this picture it is already partially pressed in. Once opened, it should look like this (below):
    Take note: the clicker on the steel band is only held on by pressure. It can fall off! Putting it back is just... putting it back. Very simply. Just don't lose it if you still want to be able to adjust your band.
    Now remove the earpad.
    IMG_0058.jpg IMG_0057.jpg
    If you haven't already done the elementary mod of removing the foam ring, do so now. Yank it off gently; if you rip it, then it's not reversible anymore (you can stick them back so they're reversible). If you've already removed it previously, I hope you kept it because you will need it in my mod! Remove the 4 screws and open it up; there's nothing holding the baffle and the cup together so utmost caution is not required.
    Here is how the inside looks like (I reversed the mods a bit to post this, so note that the blue tack is already there, as well as a circular mark for the foam rings).
    I did not do anything on the baffle side; it would be very easy to build upon this mod and add blue tack there to further tame the bass, etc. For the blue tack on the cup side, you will notice initially the center rectangle is lifted higher than the rest of the cup. Take half a stick of tack for each upper and lower side of the cup. The tack should level flat with the rectangular center, and also flatten out at the extremities. This was as far as my first mod went; you can stop here for simply reducing some bass.
    Next step: see the two screws? The hold the cup to the headband. Unscrew them. Once done, push the headband sideways to pop out the cover like so (left):
    IMG_0060.jpg IMG_0061.jpg
    The picture to the right shows the pieces you just freed. Now that that's out of the way, it will be easier to work with the cups. The cover on the exterior will no longer be used; you can store them away. Note that this may cause you to lose some isolation. If you like to have an airy soundstage, remove that cover and you can put everything back together. This was the end of my second mod.
    While the soundstage increased almost dramatically, I found it a bit too unrestrained. It has it's benefits, but I wanted to try something different. I took a fibrous sheet that I got from work and cut them into small rectangles and folded them up. You can use foam too, it will look nicer.
    I cut out about 2cm x 8cm and cut them into 8 strips. You should be able to figure out how I split them.
    Now with the pieces folded over a few times, use a flat head screw driver to place them in.
    The folded side went in the cups. much easier to work this way. You -could- do it from the inside out, makes little difference. They will stick out a bit on the inside but that is fine. Filling these holes up will bring the airflow a bit back like the way it was originally. I may have put too thick of an amount in there... try with different combinations to not lose too much soundstage.
    By the way, see where the bass ports are? they practically blocked usually...
    Now flip the cup over and grab those foam rings you removed earlier.
    Place them like this around the center of the inner-cup. Press it down a bit so it is held well by the blue tack. Remember to use adhesive side down--the shape will be more uniform this way. The mod is done!
    To put the whole thing back together, remember to put things back in the same orientation.
    See the protruding part? This is the lock mechanism, to keep the cup from pushing further into the plastic hinge. Make sure it's aligned; you can try holding them together by hand and moving it.
    The pads also have sides. I actually never noticed it until taking it apart to take these pictures! It's not very obvious on the pictures, but there is likely to be one side thicker than the other on the flaps... the nook you see on the headphone can be used to facilitate putting the pads back.
    And voila! The end result.
    As you can see, the piece holding the hinge to the cup is exposed as the cover has been removed. This piece is pretty strong though, so I don't think you will have any problems with it unless you bang it hard?? I think the hinges would break first still!
    As for the sound, it might take a bit of time to get used to since it feels pretty different from stock, especially after placing the foam ring inside the cups. Overall I'd say they sound a good deal better :wink: satisfaction not guaranteed however.
    Well, since these cans aren't exactly super popular and all, and break easily, I know this thread may as well end up a wasteland. If any of you out there with these headphones want to try it out though, feel free to! I think for the current going price, they are pretty worth it. I bought it not long after it's release!! the price difference today is just amazing...
    The absolute ease to work on these phones is great I think, and I believe they may have more potential than I've even reached. Well, enjoy modding and enjoy the new sound!
  2. Jun Raito
    Good job bro!! I'd love to know about how these blue tack mods affects overall aspects on the headphone.
    Tell me if I wrong, but what I got is some simple logic like this: More blue tack = More calmer bass.
    (I'm still not doing this kind of mod yet, so I still don't know. Besides, the blue tack thing is not cheap in country, about 5$ I guess)
    But personally I'm still guessing about another parameter like mids or high freqs. Are these improved?
    From the design, seems HA-M750 is a "closed" type. My Headphone (RP-HTX7) is a "closed" type too.
    I've tried a bit experiment about external/ body holes just like you do and there is the result:
    More opening / holes >> more air movement, less air pressure >> more soundstage, more "bright" tone
    Less opening / holes >> less air movement, more air pressure >> less soundstage (more "flat" characteristic), less "bright", add darker / bass tone.
    Another reference is some reviews about "open" headphones that says that these pairs have better soundstage than the "closed" ones. Maybe ^this^ is the explanation....
    Btw, thanks for drop by at my thread before  [​IMG]
  3. kalbee
    Wow haha, this was really an old old thread of mine.
    Yes, blue tack seems to have cleared a bit of the bass for me, but part of it might have to do with the slight change in shape on the interior.
    5$ for blue tack?? that's pretty expensive. Here it's about half of that, but it depends on the amount you buy. See if you can find some at something equivalent to a dollar store, there is a bit less in amount but more than enough for 1~2 projects.

    Yes, opening them up in the back did increase soundstage from memory. Now I don't quite remember if it stands for dynamics as well as planar magnetics (which are far more sensitive to what is changed in the cups) but increasing the vents to some extent will increase the bass too.
    I also have to add that low frequencies from external sources (such like the bus) were whistling through those opened holes. I forgot the actual frequencies but something like 50Hz was becoming 1.5kHz.

    All in all, I'd say this mod of mine might need a bit of re-examination. A lot of these used information gathered from other threads, and the changes did seem pretty real to me and my brother, who saw none of the modding process. The reason I am saying this is because my mods with another pair of dynamic headphone, along with FR measurements, show very little to no changes in terms of frequency spectrum by damping the cups. Whether or not it is because the HA-M750 have angled drivers, or because my other pair has very small cup volume in comparison, I do not know. Or that the changes are simply more in terms of decay rather than the balance in the spectrum.

    But at this point I do realize that it is pointless to convince people that these mods work. Skeptics will remain skeptics for as long as they could. If you can manage to get a permanent placebo for the better, then that may as well work out for us. :D
  4. Jun Raito
    It's not a placebo anymore, it surpasses ATH M50 already! [​IMG]
    The main idea of opening or closing these external holes is to get desired air pressure (also related with overall air volume in the cup). If it got right, you can got both deep bass and better staging
    I just wonder if my cups configuration also works on other closed headphone with angled driver......
    These are my founding about external holes location:
    Bass hole for lower excess bass parameter,  upper hole for lower excess upper parameter.
    Just don't open the middle (front section) for better clarity......

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